[SQL][DOC] Date type in SQL programming guide

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #3535 from adrian-wang/datedoc and squashes the following commits:

18ff1ed [Daoyuan Wang] [DOC] Date type

(cherry picked from commit 5edbcbfb61703398a24ce5162a74aba04e365b0c)
Signed-off-by: Michael Armbrust <michael@databricks.com>